What it does in the body
- Universal solvent for biochemical reactions
- Nutrient transport and waste excretion
- Thermoregulation (sweating, evaporative cooling)
- Blood volume and pressure maintenance
- Joint and organ lubrication (synovial fluid, cerebrospinal fluid)
How much you need (Daily Value)
| Group | Recommended | Source |
|---|---|---|
| Adult male | 3.7L/day total water (from all beverages and food) | IOM AI |
| Adult female | 2.7L/day total water | IOM AI |
| Pregnancy | 3.0L/day | IOM |
| Children | 1.0-2.4L/day depending on age | IOM |
| Older adults | Same as adults but higher risk of inadequate intake due to reduced thirst; proactive monitoring needed | IOM/ESPEN |
Richest food sources
| Food | Amount | Where |
|---|---|---|
| Cucumber | 96g water per 100g | global |
| Watermelon | 91g per 100g | global |
| Oranges | 86g per 100g | global |
| Lettuce | 95g per 100g | global |
| Tomato | 94g per 100g | global |
| Coconut water | 95g per 100g (with natural electrolytes) | southeast-asia |
| Yogurt | 85g per 100g | global |
| Buttermilk (chaas/lassi) | 90g per 100g | south-asia |
If you don't get enough
Mild: Thirst, dry mouth, dark urine, mild headache, reduced concentration (1-2% body mass deficit)
Moderate: Significant fatigue, dizziness, rapid heartbeat, reduced urine output, decreased exercise performance (3-5% deficit)
Severe: Confusion, delirium, organ failure, seizures, death (>10% body mass deficit can be fatal)
Time to onset: Mild symptoms within hours of inadequate intake; severe dehydration can be fatal within 3-5 days without any water intake
Too much
Upper limit: Kidneys can excrete ~0.8-1.0L/hour maximum. Water intoxication (hyponatremia) occurs with intake exceeding excretion capacity, typically >6L over a few hours
Hyponatremia (<135 mEq/L): nausea, headache, confusion. Severe (<120 mEq/L): seizures, cerebral edema, death. Exercise-associated hyponatremia affects marathon runners who overhydrate
How well you absorb it
Near 100% absorbed in GI tract (stomach and small intestine); very rapid (up to 1L/hour from empty stomach)
Helped by: Electrolytes (sodium enhances water absorption via SGLT1 co-transport — basis of ORS), Small frequent sips (better absorbed than large boluses), Cool temperature (absorbed faster than warm)
Hindered by: Osmotic diarrhea (reduces net absorption), Vomiting, High altitude (increased insensible losses), Alcohol and caffeine (mild diuretic effect)
Cooking & storage
Cooking adds water to dried foods (rice, pasta, beans absorb water during cooking) and drives off water from fresh foods (vegetables lose water during sauteing/roasting). Soups and stews are excellent hydration vehicles. Boiling can leach water-soluble nutrients.
Nutrisize Health totals every nutrient from what you actually eat, against targets set for your age and sex, and flags what's short — across 4,995 foods, on your device.
